Lung development involves an intricate genetic hierarchy of pattern formation genes, transcription factors, hormones and growth factors, and the extracellular matrix that co-ordinate lung branching morphogenesis and exchange. This proposal focuses on the role of pro- and anti-angiogenic growth factors, the glycosaminoglycan hyaluronan (hyaluronic acid, HA) and it s receptors CD44 and RHAMM, in both embryonic vascular and postnatal alveolar development. Preliminary data demonstrate that 1). Vascularization of lung bud explants can be stimulated by exogenous bFGF, VEGF and low molecular weight HA, 2). HA, CD44 and RHAMM regulate endothelial cell functions and angiogenesis, 3). Postnatal hypoxia decreases endothelial cell content and inhibits alveolization in association with increased TGFbeta, and 4). Normal alveolizaton is restored in the face of hypoxia with anti- TGFbeta antibody treatment or in CD44 and beta6 integrin subunit null mice that fail to activate TGFbeta. Using these models, we will test the hypothesis that pro- and anti-angiogenic growth factor signals that are regulated by hyaluronan and its receptors direct lung vascular and postnatal alveolar development. Aim 1 will characterize the developmental and postnatal expression of HA and its receptors in relation lung vascular development and alveolization in wild type, as well as CD44 and RHAMM null mice. Aim 2 will focus on growth factor and HA regulation of lung Vascularization and examine the contribution of HA and its receptors using embryonic lung bud explants, exogenous VEGF, bFGF, HA oligosaccharides and a variety of blocking agents that interfere with HA receptor function. Aim 3 will examine the role of TGFbeta, HA and its receptors in postnatal alveolar development in the face of hypoxia, dexamethasone and/or retinoic acid using blocking antibody to TGFbeta and knockout mice that fail to activate TGFbeta. Since CD44 and RHAMM are ubiquitously expressed, Aim 4 will determine the effects of cell-specific knockouts of CD44 and RHAMM on both embryonic lung Vascularization and alveolar development. In the proposed studies, lung structure will be defined using MRI imaging, computer-generated 3-D reconstructions, and histologic morphometry. Lung function will be determined using non-invasive plethysmography and exercise testing. The experiments described in this proposal will define the contribution of growth factors, HA and its receptors to pulmonary vascular development and ultimately to alveolar formation and pulmonary function. Understanding of the regulation of lung Vascularization will provide new insights into and may lead to novel approaches for augmenting lung Vascularization and alveolization.